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National Advisory Committee for Aeronautics, Technical Notes - The Shearing Rigidity of Curved Panels Under Compression

Experiments Were carried out_at Polytechnic Institute of
Brooklyn Aeronautical Laboratories in order to determine the
shearing rigidity of curved panels under compression, partic-
ularly in that region of loading where the panels are in a a”
buckled state. For the preliminary tests four, afidnfor the '
final test series eight, circular cylinders were built of
aluminum alloy sheet. The cylinders were reinforced with a
number of stringers and rings. The tests Were made by meas-
uring the angle of twist of the cylinder caused by known
amounts of torque while the cylinder was subjected to uniform
axial compression. '

It was found that the shearing rigidity decreases with
increasing compression, and the lowest value measured was
about one~tenth of the original value. The results of the
investigation are presented graphically and by means of an
approximate empirical formula. Use is made of the nondimen-
sional parameters 5 /eor and r/d, where e is the axial
compressive strain in the stringers, Ecr its value when the
panel buckles, r the radius of the cylinder, and d the
stringer spacing measured along the circumference. In the
experiments the value of Elecr varied approximately from
O to 15, that of r/d from 1 to 2.5.

While two other-research projects were being carried out
at Polytechnic Institute of Brooklyn Aeronautical Laboratories
it was found that it Would be desirable to investigate the
variation with increasing compressive stress of the shearing

rigidity of curved panels which are in a buckled state be—
cause of the compression. One of these projects dealt with
the calculation of the stress distribution in monocoque cyl—
inders (reference 1). Because of the lack of data on the
shearing rigidity the calculations had to be restricted to
cases of loading in which the panels Were in a non-buckled
state and thus a comparison with test results (reference 2)
Was possible only for low load conditions.